<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Document</title>
  </head>
  <body>
    <ul id="myList"><li>苹果</li>
      <li>橙子</li>
      <li>橘子</li>
    </ul>
    <ul id="op"></ul>
    <button onclick="myFunction()">点我</button>
    <script>
      function myFunction() {
        var item = document.getElementById('myList').firstChild;
        var cloneItem = item.cloneNode(true);
        document.getElementById('op').appendChild(cloneItem);
      }
    </script>
  </body>
</html>